CHICAGO (WLS) -- Building a park on top of a parking garage is an engineering question whose answer rests with the new Maggie Daley Park on Chicago's lakefront.
In the shadow of towers made of concrete and steel, there are building blocks of a different sort. Thousands of them are being layered together to give shape to what will be Maggie Daley Park.
"We're going to transform what was a flat, sort of uninviting area into a gem for Chicago that compliments Millenium Park," said Chicago Park District CEO Michael Kelly.
That transformation has a lot to do with topography. When this 20-acre park is done, its northeast corner will sit 30 feet higher than the southwest. That's a lot of dirt. And dirt weighs a lot. And a lot of weight would not be welcome atop the two story parking garage that sits directly underneath. So, what do you use? Geofoam.
"Geofoam is essentially Styrofoam. It's lightweight fill," Kelly said
It's 100 times lighter than soil. Geofoam isn't a new concept. It was used here before, but there's a lot more of it now, 75,000 cubic yards of it will be sculpted and tacked down to create a rolling terrain.
On top of the geofoam goes the dirt which will be deep enough in spots to accommodate the roots of one-thousand new trees. If you'd never seen the geofoam going in, you'd never know it was there.
"That's essentially the best compliment we could get once this park is open and that is that people don't realize that it's a park constructed on top of a garage," said project engineer Nichole Sheehan. "It's a park that people are going to love and hopefully come to all the time."
The park district has been recording its birth with time lapse camera, from barren garage roof to the building of baby hills, and when the park's soft opening comes next fall, this is the vision. Three of the 20 acres devoted to a children's playground. Just up the path, a 25 foot climbing wall, and when the cold months come, a feed of built in refrigerant will convert that path into a 400 meter ice skating ribbon - attracting old Hans Brinkers or perhaps young Blackhawks.
From debris dating back to the great Chicago fire to geofoam, this piece of Chicago has undergone remarkable change over the years.
In the late 40's and early 50's, there were lots of railroad, lots of parking that over the years goes went away or went underground.
"Somewhere way down there, there's fill," Kelly said. "There's probably some old railroad scrap. Now we're standing on geofoam and we're building a green park. We're building a 20 acre green roof is essentially what we're doing with a thousand trees."
The first of the trees come soon. The grand opening of Maggie Daley Park comes next Spring. Its birthing thus far carries four words welcomed in urban re-design.
Maggie Daley Park carries a roughly $55 million price tag. Most of that comes from parking garage lease money and private contributions along with five million in park district capital funds.